In SI engines for higher thermal efficiency

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ESE Mechanical 2013 Official Paper - 1
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  1. Compression ratio should be high
  2. Heat liberation during combustion should be maximum
  3. Surface to volume ratio should be high
  4. Long flame travel distance

Answer (Detailed Solution Below)

Option 1 : Compression ratio should be high
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ST 1: UPSC ESE (IES) Civil - Building Materials
20 Qs. 40 Marks 24 Mins

Detailed Solution

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Explanation:

The thermal efficiency of the Otto Cycle:

Compression ratio: r = v1/v2

Conclusion:

From the above equation, it can be observed that the efficiency of the Otto cycle is mainly the function of compression ratio for the given ratio of Cp and Ci.e. ratio of specific heats.

The thermal efficiency of the theoretical Otto cycle increases with an increase in compression ratio and specific heat ratio but is independent of the heat added (independent of load).

The efficiency of the Otto cycle is given by

As  and Hence .

Option (b), (c) and (d) are the knock parameters.

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